1. Field of the Invention
This invention relates to small, high energy density batteries and how to make them. It relates to using thin sheets of plastic material coated with thin layers of dissimilar metals, which act as cathode and anode, so as to form a bipolar battery element. Also, it relates to coating the cathode and anode layers with thin layers of cathode-active and anode active material, respectively. It relates to tightly winding these layers; together with a separator plastic layer so as to have a high energy density battery.
2. Prior Art
Secondary lithium batteries have a much higher energy density than conventional batteries, such as lead-acid or Ni--Cd batteries, because of a high electrode potential and the lightweight of the lithium. Lithium, however, shows poor rechargeability in an organic electrolyte. The charge-discharge cycling efficiency of lithium is low. Although lithium can be used to make a high-energy battery, the high activity of lithium can also make the battery unsafe.
Xie et al., as part of the active cathode material (U.S. Pat. No. 5,750,288), used a transition metal nickel together with a non-transition metal selected from the group consisting of aluminum, gallium, tin and zinc. Instead of LiNiO.sub.2, the combination Li.sub.x M.sub.y O.sub.z was used. The purpose was to increase the number of rechargeable cycles and to improve safety. Saidi et al. (U.S. Pat. No. 5,851,696) used a vanadium oxide nonmetal negative electrode (anode) instead of a solid lithium metal anode. This was done for manufacturing ease and to achieve a large discharge capability while maintaining integrity of the anode over a prolonged life cycle. Li et al. (U.S. Pat. No. 5,733,681) used a lithium manganese oxide cathode for a non-aqueous battery. Lithium manganese oxides are less of a toxicity concern and are relatively inexpensive.
Secondary lithium batteries using polymer electrolytes offer advantages over lithium ion batteries with liquid electrolytes, such as enhanced safety, long-cycle life, high energy density and flexibility. Composite electrodes for secondary lithium polymer batteries typically contain an electrode material providing active mass and a polymer electrolyte providing mechanical integrity and ionic conductivity. High conductivity for ions and electrons is needed for a high rate operation of the lithium battery. Good mechanical strength is necessary for processing and manufacturing. Prior art examples include Gozdz, et al. (U.S. Pat. No. 5,620,811) who used polyvinylidene fluoride; other polymers included in this survey are polyethylene oxide and polyacrylonitrile. Scrosati et al. (U.S. Pat. No. 5,645,960) formulated a thin film polymer battery having a flat discharge curve with either Li--Ag.sub.2 WO.sub.4 or Li--Cu.sub.2 WO.sub.4.